A field-effect transistor (FET) may be designed to have a particular threshold voltage (Vt). For example, the transistor may have a low threshold voltage (LVT), a standard threshold voltage (SVT), or a high threshold voltage (HVT). The particular threshold voltage chosen for a transistor may depend on the speed or power characteristic desired.
In bulk silicon (Si) technology, transistors having the various threshold voltage flavors may be created by varying channel doping (e.g., well, Vt-adjust, halo).
Unfortunately, channel doping is not well-suited to thin-body devices such as a fin FET (FinFET) or a quantum well FET (QWFET). Therefore, gate length tuning (Lg-tuning) or gate work function tuning may be used to modulate threshold voltage for those devices.
For a p-type FET (PFET), a silicon germanium (SiGe) channel may be used to decrease the threshold voltage. Indeed, the valence band (VB) in the SiGe moves up with regard to silicon.
All in all, threshold voltage tuning is generally well established for silicon (Si) complimentary metal-oxide-semiconductor (CMOS) devices.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.